Liquid crystal display devices are increasingly used in watches, calculators, various measurement instruments, automobile panels, word processors, electronic organizers, printers, computers, televisions, clocks, advertising boards, etc. Representative examples of the liquid crystal display mode include twisted nematic (TN) mode, super twisted nematic (STN) mode, and vertical alignment mode or in-plane-switching (IPS) mode that uses thin film transistors (TFTs). Liquid crystal compositions used in such liquid crystal display devices are required to be stable against external stimuli such as water, air, heat, and light, be in a liquid crystal phase in a temperature range as wide as possible around room temperature, have low viscosity, and operate at low drive voltage. A liquid crystal composition is constituted by several to several dozens of compounds in order to optimize dielectric anisotropy (Δ∈) and/or refractive index anisotropy (Δn) and the like for each individual display device.
A vertical alignment (VA) mode display uses a liquid crystal composition having negative Δ∈ whereas a horizontal alignment mode display, such as TN, STN, or in-plane-switching (IPS) mode display, uses a liquid crystal composition having positive Δ∈. Also reported is a drive mode by which a liquid crystal composition having positive Δ∈ is aligned vertically in the absence of applied voltage and driven by applying a horizontal electric field to perform display. The demand for liquid crystal compositions having positive Δ∈ is increasing. Meanwhile, low-voltage driving, high-speed response, and a wide operation temperature range are desirable in all drive modes. In other words, Δ∈ is required to be positive and have a large absolute value, the viscosity (η) is required to be small, and the nematic phase-isotropic liquid phase transition temperature (Tni) is required to be high. There is also a need to adjust the Δn of the liquid crystal composition in accordance with a cell gap so that the setting of Δn×d, which is the product of Δn and a cell gap (d), is met. Furthermore, high-speed response is important in using a liquid crystal display device in a television or the like. Thus, a liquid crystal composition having a low rotational viscosity (γ1) is required for this use.
An example of a high-response-speed-oriented liquid crystal composition has been disclosed which contains a liquid crystal compound having positive Δ∈ represented by formula (A-1) or (A-2) used in combination with a liquid crystal compound (B) having neutral Δ∈. It is well known in the field of liquid crystal compositions that the feature of these liquid crystal compositions is that the liquid crystal compound having positive Δ∈ has a —CF2O— structure and that the liquid crystal compound having neutral Δ∈ has an alkenyl group (PTL 1 to PTL 4).

Expansion of applications of liquid crystal display devices has caused great changes in the way these devices are manufactured and used. In order to meet these changes, optimization of characteristics other than basic physical property values previously considered has become necessary. Namely, VA and IPS mode liquid crystal display devices that use liquid crystal compositions have become widespread, and supersize display devices 50 or greater have become commercially viable and used. With the increase in substrate size, the mainstream injection method for injecting a liquid crystal composition into a substrate has shifted from a vacuum injection method to a one-drop-fill method (ODF); however, this leads to a problem of degradation of display quality caused by drop marks that occur at the time the liquid crystal composition is dropped onto the substrate. Moreover, in a liquid crystal display device production process that employs the ODF method, optimum amounts of liquid crystals need to be dropped in accordance with the size of the liquid crystal display device. Once the injection amount increases from the optimum value, the previously designed balance between the refractive index of the liquid crystal display device and the driving electric field is lost and display defects such as generation of nonuniformity and contrast failures result. In particular, the optimum liquid crystal injection amount for small-size liquid crystal display devices frequently used in latest smart phones is small and it is difficult to control the deviation from the optimum value within a particular range. Accordingly, in order to keep the yield of liquid crystal display devices high, for example, a liquid crystal composition is required to be less susceptible to impacts and rapid pressure changes inside the dropping machine during dropping of liquid crystals and to have properties that allow liquid crystals to be dropped stably over a long period of time.
As described above, a liquid crystal composition for use in an active matrix-driving liquid crystal display device driven by TFTs and the like is required to maintain those properties and performance, such as high-speed response, required by liquid crystal display devices, exhibit high resistivity, high voltage holding ratio, and stability under external stimuli such as light and heat which have been previously considered important, and be developed by considering the liquid crystal display device production method.